Deployment validation error: 'Value cannot be null. Parameter name: con'

## Description
I'm trying to deploy an Azure KeyVault from a Bicep template.
When validating the template using the REST API, the server responds with the error `"The request content was invalid and could not be deserialized: 'Value cannot be null.\r\nParameter name: con'."` I have no idea where the parameter `con` comes from and how I can set it.

This problem occurs since last Friday (27th of January, 2023) and also occurs on some other deployments, such as a local network gateway but not on all. For example, storage account, application insights and web app service deployments work okay.

This error occurs in every possible way of deployment:
- AzureResourceManagerDeploymentTaskV3 in Azure Devops pipeline
- az cli deployment from local machine
- cURL call to the REST API validation endpoint

## Details
I captured the the az cli command debug output: [debug_arm.txt](https://github.com/Azure/azure-rest-api-specs/files/10534652/debug_arm.txt)

And these are the template and parameter files (added `.txt` extension so I could upload them here):

- [keyVault.bicep.txt](https://github.com/Azure/azure-rest-api-specs/files/10534677/keyVault.bicep.txt)
- [vaults.bicep.txt](https://github.com/Azure/azure-rest-api-specs/files/10534740/vaults.bicep.txt)
- [keyVault-rg-datawarehouse-dev.parameters.jsonc.txt](https://github.com/Azure/azure-rest-api-specs/files/10534753/keyVault-rg-datawarehouse-dev.parameters.jsonc.txt)

Even without generating the resource name using the `EdsnUtilities-resourceName` template, this error occurs.

Start by reviewing debug_arm.txt and reproducing validation with keyVault.bicep.txt, vaults.bicep.txt, and keyVault-rg-datawarehouse-dev.parameters.jsonc.txt. Compare the failing Azure Key Vault and local network gateway deployments with the working deployment examples, then trace whether the null `con` error originates in this repository or the Azure validation service; done means identifying the responsible API behavior and documenting a confirmed fix or escalation.

Written by the indexing model from the issue text.